Optical Sensor Solder Resist Pattern for Accurate Mounting
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Solution Overview
Problem
Conventional small COB-type optical sensors face challenges in mounting the bare chip surface visible from the opposite surface, leading to insufficient solder fillet formation and deformation of protective acrylic resin due to solder flow along the pattern, making it difficult to position the sensor correctly.
Innovation Solution
The optical sensor design incorporates a pattern partially covered with solder resist to prevent solder flow and uses a through-hole configuration to allow the sensor to be mounted with the bare chip surface visible from the opposite side, ensuring accurate solder fillet formation and protecting the transparent acrylic resin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the sensor is mounted with the bare chip mounted surface visible from the opposite surface, then light reflected by pad, gold wire, and component is reduced, but solder flow along the pattern causes insufficient solder fillet formation and deformation of protective acrylic resin
Solution Approach 1:
The circuit board is divided into two surfaces with distinct functions: the first surface (bare chip mounted surface) is optimized for electrical connections and component mounting, while the second surface (opposite surface) is optimized for light detection with minimal reflective elements. This segmentation allows the sensor to be mounted with the bare chip surface visible from the opposite side, reducing light reflection interference while maintaining proper soldering on the component side.
Solution Approach 2:
The pattern is designed with different properties in different regions: on the first surface, the pattern provides electrical connection pathways, while on the second surface, the pattern is configured to minimize light reflection. The solder resist is selectively applied to specific regions of the pattern to control solder flow locally, preventing deformation of the protective acrylic resin while ensuring adequate solder fillet formation at connection points.
2Measurement precision
If the bare chip mounted surface is made visible from the opposite surface, then mounting accuracy is enhanced and stray light interference is reduced, but solder flow along the pattern causes insufficient solder fillet and acrylic resin deformation
Solution Approach 1:
Solder resist is applied to the pattern in advance before soldering, specifically in regions where solder flow might cause harmful effects. This preliminary protective action prevents solder from flowing along the entire pattern, thereby preventing deformation of the protective acrylic resin while still allowing adequate solder fillet formation at the terminal connections, ensuring both mounting accuracy and soldering reliability.
Solution Approach 2:
Solder resist acts as an intermediary substance between the solder and the pattern/acrylic resin. It selectively blocks solder flow in regions where it would cause deformation of the protective acrylic resin, while permitting solder adhesion at the terminal connections. This intermediary layer enables the bare chip surface to be visible from the opposite surface for improved light detection accuracy without compromising solder bonding reliability.
3Object-affected harmful factors
If the sensor is mounted with components on the opposite surface, then light reflection is reduced, but the pattern is exposed to solder flow causing manufacturing defects
Solution Approach 1:
The circuit board is segmented into two functional surfaces: the first surface (bare chip mounted surface) contains the electronic components and electrical patterns, while the second surface (opposite surface) is configured for light detection with minimal reflective elements. This segmentation allows the sensor to be mounted with the bare chip surface visible from the opposite side, reducing light reflection interference while confining solder flow hazards to the component side where they can be controlled by solder resist.
Solution Approach 2:
Solder resist serves as an intermediary barrier between the solder and the pattern on the bare chip mounted surface. It selectively prevents solder from flowing along the pattern traces that would expose them to solder flow and cause deformation of the protective acrylic resin, while still allowing solder to adhere properly at the terminal connection points. This intermediary protection enables the desired mounting orientation that reduces light reflection.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables stable solder bonding and prevents deformation of the acrylic resin, allowing the sensor to be mounted with the bare chip surface visible, enhancing mounting accuracy and reducing stray light interference in light detection.
Implementation Method 1
a portion of the pattern between the protection member and the terminal portion is covered with solder resist
Implementation Method 2
bare chips including a photodiode 104 as a light receiving element
Data Source
AI summary
An optical sensor includes a bare chip mounted on a circuit board, a protection member configured to protect the bare chip, a pad connected to the bare chip via a wire, and a pattern connecting the pad and a terminal portion at an edge of the circuit board to each other. The pattern is connected to the terminal portion on a same surface as a surface on which the bare chip is mounted, and a portion of the pattern between the protection member and the terminal portion is covered with solder resist.